~ Musings on weather and science

PDO…Final Chapter

A dry, sunny and warm weekend is on tap for the Truckee Meadows. The west coast ridge of high pressure is staying in place, and temperatures will run from the mid-50s into the low 60s throughout. The next chance of rain comes a couple of days into next week, when a weak low moves up from the south. Unfortunately, that is not a very encouraging pattern to give us more than at most scattered showers.

Knowing ocean temperature phases helps, but it’s not the whole story.

While the state of ocean temperatures in one region (such as the PDO or El Niño) can have a lot to do with the weather in other places, it’s never as simple as a one to one relationship. Teleconnections are the interworkings between various large scale anomalies in various ocean basins, which together influence atmospheric patterns. Besides the PDO and ENSO (El Niño), you also have other oscillations in other parts of the globe, including the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO) and the Pacific-North America Index (PNA.) All of these not only affect the regions in which they occur, but interact with patterns affected by the others to make forecasting very far down the line very difficult.

Chaos theory states if a butterfly flaps his wings in Tokyo, it could result in rain a week later in New York. Essentially, it says that small perturbations in one place can amplify to very large perturbations (storms) somewhere else. Certainly, whole ocean temperature profiles equal a lot of butterflies, so one has to be careful to just look at one ocean temperature profile (like El Niño or the PDO) and assume what weather will result from it. In general, a positive PDO phase will make the southwest US a little wetter, but it doesn’t happen quickly, and there are a lot of other factors (teleconnections) that also factor into the pattern.

Generally we have been in a cold phase of the PDO the last several years, but just flipped over to a positive phase in 2014. (Courtesy NOAA Fisheries.)

Hopefully we will stay in the positive PDO a while longer, and will get some help from the other ocean basins soon.